Probably because they're concentrating on the tools and not the operating system. The O/S isn't hugely important as long as it is capable of running the tools (and is capable of being secured from an attack), and personally, I would prefer them to get the toolset right and correctly installed/integrated into the distro than to always chase the latest Linux release.
Having said that, I would hazard a guess that they're basing their O/S releases on the LTS versions of Ubuntu, and will probably be working on a 12.04 base for the next version.


